In a wireless transmission system that transmits the same information in parallel using two or more different types of modulation schemes, such as a satellite-based digital audio transmission system transmitting two TDM signals and a single OFDM signal, a receiver processes the differently modulated signals to generate separate demodulated signals that are then combined to form a single combined signal for further processing (e.g., decoding). In one embodiment, the receiver applies a maximal ratio combining (MRC) technique to generate a single optimal ratio combined signal from the differently modulated signals. By combining the differently modulated signals using an MRC technique, the adverse affects of noise related to inter-symbol interference in the individual signals can be reduced and the complexity of hardware in the receiver can be reduced.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A transmitter, comprising: (a) an encoder to add redundancy to a data sequence; (b) an interleaver connected to the encoder to output encoded symbols as interleaved symbols in data frames; (c) an inserter connected to the interleaver to insert synch bits into data frames to generate synchronized data, of which copies of the synchronized data undergo further processing; (d) a first modulator for modulating a first copy of the synchronized data to generate a signal having a first modulation scheme; and (e) a second modulator for modulating a second copy of the synchronized data to generate a signal having a second modulation scheme.
2. The transmitter of claim 1 , wherein: the first modulator is a DQSPK modulator and the first modulation scheme is OFDM.
3. The transmitter of claim 1 , wherein: the second modulator is a QSPK modulator and the second modulation scheme is TDM.
4. The transmitter of claim 1 , further comprising a third modulator for modulating a third copy of the synchronized data to a generate a time-delayed signal having a third modulation scheme.
5. The transmitter of claim 4 , wherein: the third modulator is a DQSPK modulator and the third modulation scheme is TDM, wherein the time-delayed signal is delayed by a delay buffer configured with the third modulator to a known delay value.
6. The transmitter of claim 1 , wherein: the first modulator is adapted to generate an OFDM signal; and the second modulator is adapted to generate a TDM signal.
7. The transmitter of claim 6 , wherein: the first modulator performs DQPSK modulation followed by a differential modulation over frequency; and the second modulator performs QPSK modulation.
8. The transmitter of claim 1 , further comprising a third modulator for modulating a third copy of the synchronized data to a generate a signal having a third modulation scheme.
9. The transmitter of claim 8 , wherein: the first modulator is adapted to generate an OFDM signal; the second modulator is adapted to generate a first TDM signal; the third modulator is adapted to generate a second TDM signal.
10. The transmitter of claim 9 , wherein the OFDM signal and the second TDM signal are time-delayed relative to the first TDM signal.
11. The transmitter of claim 10 , wherein: the first modulator comprises a delay buffer followed by a DQPSK modulator followed by a frequency interleaver and difference modulator, followed by an inverse fast Fourier transform (IFFT), followed by a guard interval block; the second modulator comprises a QPSK modulator followed by an equalizer training sequence inserter followed by an intermediate frequency (IF) modulator; and the third modulator comprises a delay buffer followed by a QPSK modulator followed by an equalizer training sequence inserter followed by an IF modulator.
12. The transmitter of claim 9 , wherein: the first modulator performs DQPSK modulation followed by a differential modulation over frequency; the second modulator performs QPSK modulation; and the third modulator performs QPSK modulation.
13. A transmitter, comprising: (a) an encoder adapted to encode input data; (b) an interleaver adapted to generate interleaved data from encoded data generated by the encoder; (c) an inserter adapted to insert synch bits into the interleaved data to generate synchronized data; (d) a first modulator adapted to modulate a first copy of the synchronized data using a first modulation scheme to generate a first modulated signal; and (e) a second modulator adapted to modulate a second copy of the synchronized data using a second modulation scheme to generate a second modulated signal.
14. The transmitter of claim 13 , wherein: the first modulator is adapted to generate an OFDM signal; and the second modulator is adapted to generate a TDM signal.
15. The transmitter of claim 14 , wherein: the first modulator performs DQPSK modulation followed by a differential modulation over frequency; and the second modulator performs QPSK modulation.
16. The transmitter of claim 13 , further comprising a third modulator for modulating a third copy of the synchronized data to a generate a signal having a third modulation scheme.
17. The transmitter of claim 16 , wherein: the first modulator is adapted to generate an OFDM signal; the second modulator is adapted to generate a first TDM signal; the third modulator is adapted to generate a second TDM signal.
18. The transmitter of claim 17 , wherein the OFDM signal and the second TDM signal are time-delayed relative to the first TDM signal.
19. The transmitter of claim 18 , wherein: the first modulator comprises a delay buffer followed by a DQPSK modulator followed by a frequency interleaver and difference modulator, followed by an inverse fast Fourier transform (IFFT), followed by a guard interval block; the second modulator comprises a QPSK modulator followed by an equalizer training sequence inserter followed by an intermediate frequency (IF) modulator; and the third modulator comprises a delay buffer followed by a QPSK modulator followed by an equalizer training sequence inserter followed by an IF modulator.
20. The transmitter of claim 17 , wherein: the first modulator performs DQPSK modulation followed by a differential modulation over frequency; the second modulator performs QPSK modulation; and the third modulator performs QPSK modulation.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
October 28, 1999
June 17, 2003
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